Separating bitumen from sand

Hot-Water A process for separating bitumen from tar sands. Developed by SUNCOR for treating the sands from Athabasca, Alberta, based on an invention made by K. A. Clarke in 1932. Two large plants were operating in Canada in 1984. 

The other aboveground method of separating bitumen from tar sands after the mining operation involves direct heating of the tar sand without previous separation of the bitumen. Thus, the bitumen is not recovered as such, but is an upgraded overhead product. 

Bitumen is separated from the oil sand matrix, in large tumblers, where surfactants play key roles in separating bitumen from mineral particles and then floating the former. As reviewed elsewhere [79, 167], from the bitumen, alkaline conditions are used to produce (saponify) a class of natural surfactants that are predominantly aliphatic carboxylates of chain length typically to and also... 

The hot water flotation process for oil sands is a separation process in which the objective is to separate bitumen from mineral particles by exploiting the differences in their surface properties. The slurry conditioning process involves many process elements as illustrated in Figure 3. Given that ablation and mixing, mass and heat transfer, and chemical reactions are accommodated, the conditioning step involves separating bitumen from the sand and mineral particles. 

Sadeghi, K. M. Sadeghi, M.-A. Kuo, J. F. Jang, L. K. Yen, T. F. Self-Propogated Surfactants Formed During Separation of Bitumen From Tar Sands Using an Alkaline Solution and Sonication, Presented at ACS, 1987 Pacific Conference on Chemistry and Spectroscopy, October 28-30, 1987. 

Adhesion Tensions and Tar Sand Extraction with Tween Surfactants. Mea-surement of the adhesion tension (t) allows the determination of the wettability of a given solid by a given liquid or surfactant solution. Measurements of adhesion tension between both bitumen or clay surfaces and various surfactant solutions is thus highly relevant to a study of the effects of surfactants in the separation of bitumen from Athabasca tar sand. 

The elemental analysis of oil sand bitumen (extra heavy oil) has also been widely reported (Speight, 1990), but the data suffer from the disadvantage that identification of the source is too general (i.e., Athabasca bitumen which covers several deposits) and is often not site specific. In addition, the analysis is quoted for separated bitumen, which may have been obtained by any one of several procedures and may therefore not be representative of the total bitumen on the sand. However, recent efforts have focused on a program to produce sound, reproducible data from samples for which the origin is carefully identified (Wallace et al., 1988). It is to be hoped that this program continues as it will provide a valuable database for tar sand and bitumen characterization. 

The raw minerals mined from natural deposits comprise mixtures of different specific minerals. An early step in mineral processing is to use crushing and grinding to free these various minerals from each other. In addition, these same processes may be used to reduce the mineral particle sizes to make them suitable for a subsequent separation process. Non-ferrous metals such as copper, lead, zinc, nickel, cobalt, molybdenum, mercury, and antimony are typically produced from mineral ores containing these metals as sulfides (and sometimes as oxides, carbonates, or sulfates) [91,619,620], The respective metal sulfides are usually separated from the raw ores by flotation. Flotation processes are also used to concentrate non-metallic minerals used in other industries, such as calcium fluoride, barium sulfate, sodium and potassium chlorides, sulfur, coal, phosphates, alumina, silicates, and clays [91,619,621], Other examples are listed in Table 10.2, including the recovery of ink in paper recycling (which is discussed in Section 12.5.2), the recovery of bitumen from oil sands (which is discussed further in Section 11.3.2), and the removal of particulates and bacteria in water and wastewater treatment (which is discussed further in Section 9.4). 

Both of the Canadian plants use the technique of hot water extraction to remove the bitumen from the tar sand. In this procedure the tar sand, steam, sodium hydroxide, and hot water are mixed and tumbled at a temperature of around 90°C. Layers of sand pull apart from the bitumen in this process. Additional hot water is added and the bitumen-sand mixture is separated into two fractions by gravity separation in cells in which the bitumen rises to the top and is skimmed off, while the sand settles to the bottom. The upgrading of the bitumen to a synthetic crude is then accomplished by oil refinery procedures including coking, in which carbon is removed by thermal distillation and hydrotreating. 

The key difference between the methods used for oil recovery from oil shales and that used for tar sands is in the methods used for separation of the organic constituent from the naturally occurring material. Oil shale processing requires the whole of the mined material to be heated to pyrolysis temperatures of 500°C or more, whereas the hot water process for tar sands extraction requires the mined tar sand (plus process water) to be heated to only around 70-80°C. Only the extracted bitumen from the tar sand, some 10-12% of the mined mass, has to be heated to ca. 500°C during the coking step to obtain synthetic crude. Because all the oil shale must be heated to pyrolysis temperatures to effect oil recovery, efficient heat transfer and... 

Of the Canadian deposits, the largest, Athabasca, is at least 4 times the size of the largest conventional oil field, Ghawar, in Saudi Arabia (5). Of the Athabasca s estimated 600 billion barrels of bitumen, about 60 billion barrels could be recovered by surface mining of the oil sand followed by beneficiation to separate the oil. Currently two commercial plants are producing synthetic crude oil from the Athabasca deposit. In these operations, the oil sands are first mined, and the bitumen is extracted by a hot-water flotation process, which produces a bituminous froth. After breaking the froth, the separated bitumen is subsequently upgraded by refineiy-type processes to produce synthetic crude oil. In order to understand the nature of the froths produced, the nature of oil-sand structure will be reviewed first, and then the flotation process from which froths are produced will be examined. 

The usual representation of oil-sand structure is shown in Figure 1, where the bitumen is not in direct contact with the mineral phase, but instead is separated by at least a thin film of water. The separation of oil from solids by a water film is widely held to be the characteristic difference between Athabasca oil sand and oil sand from other oil-sand deposits in the world (e.g., California, New Mexico, or Utah). These other oil-sand deposits are thought to consist of oil-wet solids. That is, the bitumen occurs in direct contact with the mineral grains. The significance of the distinction is that the oil-wet oil sands are considered to be more difficult to beneficiate using hot-water flotation because of the difficulty in dislodging bitumen from an oil-wet surface. 

Schramm, L.L. (1988) Use of a submersible viscometer in the primary separation step of the hot water process for recovery of bitumen from tar sand, Canadian Patent 1,232,854, Feb. 16,... 

Previous workers have employed several biosurfactants to release bitumen from tar sand of ambient temperatures. It was observed that during the "cold water" separation process, these biosurfactants can significantly improve the yield of bitumen in a pilot-plant. 

Disengagement of bitumen from solids wiU be favoured if their respective surfaces can be made more hydrophilic since a lowering of surface free energy will accompany the separation. The phase separation is enhanced by the effects of mechanical shear and disjoining pressure. Adopting the water-wet model for Athabasca oil sand, one has that a thin aqueous film already separates the bitumen from the sand. So this preexisting separation needs only to be enhanced. 

From an operational perspective, naphthenic acids are both beneficial and potentially a concern. As has been discussed earlier, the surface active properties play an important role in the efficiency of the bitumen separation methods from oil sands. These same surface active properties result in toxic responses to an array of biota that may affect the water... 

Another source of oil is oil shales and tar sands which require special processing to extract the oil. Tar sands are found throughout the world, and deposits are known to exist in 49 countries. Major deposits are found in Venezuela and Canada. Alberta s tar sands contain an estimated 9 x lO bbl of crude bitumen from which about 3 x 10 bbl of synthetic crude oil can be obtained. The tar sands consist of particles of sand held together by a water and oil coating as shown in Fig. 3.4. The process by which the oil is separated from the water and sand involves subjecting the mixture to hot water and steam and skimming off the oU. Since over 90% of the oil sands cannot be surface mined... 

Flotation or froth flotation is a physicochemical property-based separation process. It is widely utilised in the area of mineral processing also known as ore dressing and mineral beneftciation for mineral concentration. In addition to the mining and metallurgical industries, flotation also finds appHcations in sewage treatment, water purification, bitumen recovery from tar sands, and coal desulfurization. Nearly one biUion tons of ore are treated by this process aimuaHy in the world. Phosphate rock, precious metals, lead, zinc, copper, molybdenum, and tin-containing ores as well as coal are treated routinely by this process some flotation plants treat 200,000 tons of ore per day (see Mineral recovery and processing). Various aspects of flotation theory and practice have been treated in books and reviews (1 9). 

Hot-Water Process. The hot-water process is the only successflil commercial process to be appHed to bitumen recovery from mined tar sands in North America as of 1997 (2). The process utilizes linear and nonlinear variations of bitumen density and water density, respectively, with temperature so that the bitumen that is heavier than water at room temperature becomes lighter than water at 80°C. Surface-active materials in tar sand also contribute to the process (2). The essentials of the hot-water process involve conditioning, separation, and scavenging (Fig. 9). 

---